1. Field of the Invention
The present invention is utilized in an ink jet type printer or recorder. The present invention is utilized in a device which includes a recording head provided with a plurality of regularly arranged nozzles from which ink droplets are selectively jetted correspondingly to an externally supplied image signal and is adapted to print characters or drawings by scanning a paper or the like with the recording head. Particularly, the present invention relates to an ink jet type recording head having a simplified construction and an increased nozzle density.
2. Description of Related Art
An ink jet type recording head operates such that a plurality (n) of nozzles, where, in a case of a multicolor recording head, n is, for example, 24 to 300 for each color, thereof selectively jet droplets correspondingly to an electric signal (printing data) and print characters or a drawing on a recording medium such as paper sheet by scanning the paper sheet along a surface thereof with the recording head. The ink jet type recording head generally includes at least one ink pool which is provided commonly for a plurality of nozzles and in which ink is reserved. Ink in the ink pool is introduced into pressure chambers through thin ink supply passages communicating with the respective nozzles and ink droplets are jetted from selected ones of the nozzles by pressurizing ink in the corresponding pressure chambers by a pressure generator for generating a pressure correspondingly to an electric signal.
When the droplets are jetted from the selected ones of the nozzles by pressurizing ink in the corresponding pressure chambers which are connected to the respective nozzles, a pressure wave is produced by the pressurization of ink in the pressure chambers and propagates back to the ink pool which is common to the pressure chambers. Such pressure wave propagation may adversely influence the ink jetting condition of other nozzles than the selected nozzles as so-called sound cross talk and, in some extreme case, the other nozzles may be caused to jet a small amount of ink.
In order to make the recording head compact, it is necessary to reduce the size of the ink pool. However, when the number of nozzles to be driven simultaneously is increased and the capacity of the ink pool is not sufficient to accommodate this, the amount of ink to be supplied from the ink pool to the pressure chambers is a insufficient and stable ink jet operation becomes impossible.
To realize stable ink jet operation regardless of the number of nozzles to be driven simultaneously by preventing sound cross-talk and the shortage of the ink supply from occurring, to make the size of the whole recording head small by increasing the nozzle density or by increasing the number of nozzles in a predetermined head size, and to fabricate the recording head at low cost by simplifying the head structure, are ever present problems associated with ink jet type recording heads.
Japanese Patent Application Laid-open No. Hei 8-58089 discloses an example of a structure of an ink jet type recording head which is constructed via lamination of a plurality of punched plate materials. FIG. 1 is a cross section of the head and FIG. 2 is an exploded perspective view of this structure. In FIGS. 1 and 2, an ink pool 30 is provided in one (101) of the plates and is used commonly by a plurality (n) of nozzles 31. Ink reserved in the ink pool 30 is introduced to ink supply passages 33 provided for the respective nozzles 31 through respective ink supply ports 32 and further introduced to pressure chambers 34 provided in another plate (104).
As shown in FIGS. 1 and 2, the ink jet recording head is constituted with a nozzle plate 100, an ink reservoir chamber or an ink pool forming plate 101, an ink supply port forming plate 102, a sealing plate 103, a pressure chamber forming plate 104 and a vibrator plate 105, which are laminated in order to form ink passages from the ink pool 30 to the respective nozzles 31. Further, the ink jet type recording head comprises an actuator constituted of piezo-electric elements 106, an upper electrode 107 and a flexible printed circuit board 108, etc.
In this structure of ink jet recording head, the nozzle 31 can be arranged in two rows in a flat plane as shown in FIG. 2. Therefore, it is possible to double the nozzle density in a sub scan direction by shifting nozzle positions in one row with respect to those in the other row. However, this structure is complicated due to the large number of the plates to be laminated and, therefore, there is a problem in the fabrication steps for machining parts in the respective plates, positioning them precisely in laminating them and adhering and/or bonding them to each other. Further, in the ink jet recording head having this structure, the ink pool 30 is arranged such that it overlaps the ink supply passage 33 only partially and does not overlap the pressure chamber 34 and the nozzle 31. Therefore, an area of the ink jet type recording head which is occupied by the ink pool is small with respect to the whole area of the ink jet type recording head and, in order to make the ink pool sufficiently large, the head must be also large.
As an ink jet recording head whose number of plates to be laminated is reduced, Japanese Patent Publication No. Hei 4-52213 discloses a structure in which pressure chambers, nozzles in communication with these pressure chambers and ink supply passages are formed in one and single plate. This structure is shown in FIG. 3, which is a cross section of the head, and FIG. 4 which is a disassembled perspective view of the same. In FIGS. 3 and 4, a piezo-electric element 114 is supported in contact with a vibrator plate 113 by a rigid member 116. This plate mechanically vibrates in response to an electric signal supplied externally through electrodes 112 and 115. The vibration of the piezo-electric element 114 is transmitted to the pressure chambers 44 through the vibrator plate 113. Thus, ink is supplied from an ink pool 117 through the ink passages 111 to the nozzles 41.
The structure of the ink jet recording head shown in FIGS. 3 and 4, is advantageous in that the number of plates to be laminated is small. However, as will be clear from FIG. 3, a precise machining of the ink pool, the pressure chambers and the nozzles, which have different configurations, in the substrate plate 40 is required, which leads to an increase of the fabrication steps. Further, in this structure, the ink pool 117 must be arranged next to the pressure chambers 44 due to which a reduction of the size of the whole recording head becomes difficult.
Japanese Patent Application Laid-open No. Hei 3-274157 discloses an ink jet recording head in which the nozzle density in a sub scan direction is made large by arranging nozzles in a matrix in plan view. However, the technique disclosed therein is related to a structure of an electro-mechanical transducer element for driving pressure chambers arranged in a matrix and is not a technique for arranging them in a matrix according ink flow.
Japanese Patent Application Laid-open No. Hei 7-246701 discloses an ink jet type recording head designed to achieve both a compact ink jet head and a reliable ink supply to all of pressure chambers. The structural arrangement of this ink jet head is shown in FIG. 5 which is a disassembled perspective view thereof and FIG. 6 which is a cross section thereof. As shown in FIGS. 5 and 6, a plurality of nozzles 97 and a corresponding number of pressure chambers 119 in communication with the respective nozzles 97 are formed and ink reserving chambers 120 for temporarily reserving ink to be supplied to the pressure chambers 119 is provided in communication with the pressure chambers 119.
Since, in this structure, the ink reserving chambers 120 can be arranged in overlapping relation to the plurality of the pressure chambers 119 in a vertical plane parallel to an ink jet head plate 118 including a front side plate 125, an intermediate plate 126 and a rear plate 127, it is superior to the structures shown in FIGS. 1 and 2 and FIGS. 3 and 4 in that a larger ink reserving chamber can be formed. However, the nozzle ports 97 and the ink supply passages 121 can not overlap the ink jet head 118. Further, in the structure shown in FIGS. 5 and 6, the ink jet head plate 118 for forming the passages from the ink reserving chambers 120 to the nozzle ports 97 has a three-layer structure. Therefore, in assembling these three plates 125, 126 and 127, a precise positioning of the ink supplies 121 and the pressure chambers 119 and a precise positioning of the pressure chambers 119 and the nozzle ports 97 formed in the two platesl25 and 126 are required, which cause the number of fabrication steps to be increased. This problem is similar to that of encountered with the structure shown in FIGS. 1 and 2.
In the structure shown in FIGS. 5 and 6, the ink reserving chamber 120, for example, is formed in the front side plate 125 by a precision machining requiring a precise depth control. Therefore, the number of fabrication steps is increased and the yield of machining of the parts is lowered. This is similar to that of the structure shown in FIGS. 3 and 4.